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Comment by rkp8000 | Hacker News Reader

It's a good question. It looks like they actually specifically check for this and show that it's not two separate groups of neurons. Instead a subset of the neural population changes their representation of the input as it moves from sensory to memory, so it's more like a single group of neurons that represents current sensory and past memory information in two orthogonal directions.

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So current sensory info is a vector of numbers, and past memory info is a vector of numbers, and these two vectors are orthogonal.

What are these numbers, precisely?

In a simple example that I can think of it could just be a vector of <present, past> aka the current info could be encoded like [<2, 0>, <4, 0>] then rotated to ("y axis") [<0, 2>, <0, 4>] allowing you to write more "present" data to the original x dimension without overriding the past data.

If you're asking about the exact numbers here's a snippet from the xlsx document. ``` ABCD_mean ABCD_se ABCD_mean ABCD_se XYCD_mean XYCD_se XYCD_mean XYCD_se day neuron subject time 0 6.012574653 0.5990308106 6.181361381 0.5737310366 6.59759636 0.6419092978 6.795648346 0.5716884524 1 2 M496 -50 ```

According to the article SEM neural activity, though this is way beyond my ability to interpret.

My simplified picture of what’s going on is something like this (if I’m understanding the paper correctly). Stimulus A starts out represented by the vector (1,1,1,1) and B by (-1,-1,-1,-1). Those are the sensory representations. Later A is represented by (1,1,-1,-1) and B by (-1,-1,1,1). Those are the memory representations. The last two component/neurons have “switched” their selectivity and rotated the encoding. The directions (1,1,1,1) and (1,1,-1,-1) are orthogonal, so you can store sensory info (A vs B in the present) along one and memory info (A vs B in the past) aling the other.

So memory and sensory get multiplexed?

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